1. Field of the Invention
This invention relates to inkers, and, more particularly, to inker apparatus for marking defective semiconductor wafer elements during and after testing procedures.
2. Description of the Prior Art
When a semiconductor wafer is tested, a plurality of probe needles engage different circuit elements on portions of the semiconductor element. The purpose of the testing is to determine or to detect defective circuits. The probe needles provide appropriate electronic signals for testing the circuit elements. If an element undertest is determined to be defective, the particular wafer element will be marked by a spot of ink. The ink is placed on the wafer element by an inker apparatus.
When the semiconductor wafer is later cut into specific die elements, the die elements with the ink dots are rejected.
A semiconductor wafer may be processed after testing, and it is accordingly highly desirable or necessary that the ink remain on the defective elements during the processing.
Since a single semiconductor wafer includes a plurality of individual elements, each of which must be tested. In on line inking, ink is placed on each defective element at intervals during the testing of the wafer. The semiconductor wafer is successively indexed under the probe needles. The probe needles remain relatively fixed while the semiconductor wafer element moves relative to the probe needles. The inker apparatus is centered relative to the probe needles and accordingly is centered relative to each individual semiconductor element on a wafer as the elements are successively indexed beneath the probe needles. The inker apparatus moves vertically as required. Ink dots are deposited after testing a particular element which failed testing criteria. The wafer if then indexed to test the next element.
Some applications place the ink dots on defective circuit elements in an off-line mode. In this mode, defective element locations are stored in an electronic wafer map during testing. The wafer maps are then used on an off-line inking station (a station without a tester) and ink dots are deposited on defective circuits as discussed above according to the electronic wafer map. This mode of operation is more efficient as it does not hold up the expensive tester during the time it takes to deposit the ink dot.
The inker apparatus of the prior art generally includes an ink reservoir lined with a needle, and ink is delivered from the reservoir and through the needle in response to the activation of a solenoid which in turn activates a plunger associated with the reservoir. One such inker apparatus is described in U.S. Pat. No. 4,992,729 (Nadeau). In the '729 apparatus, the solenoid is generally parallel to the ink reservoir.
Another type of inker of the prior art uses gas pressure to force the ink out of a reservoir. This type of inker is generally referred to as a "pneumatic" inker.